Articles for retail display such as bathroom tissue, paper napkins, or household towel Products are commonly packaged in heat-sealed plastic film. Packaging utilizing a plastic film such as polyethylene is formed by wrapping the package in a sheet of plastic film and heat sealing the length-wise seam of the package. End folds are formed in the film and sealed to one another on both ends of the package to fully seal the package. Apparatus for performing this packaging operation must be able to rapidly process a great number of packages while at the same time maintaining the end fold shape and integrity to present a neat and clean store shelf appearance to consumers. Furthermore, the end folded film must be welded to itself but may not adhere to the packaged article.
A typical conventional end fold sealer receives packages from an overwrapping machine which have been wrapped in plastic film with the long girth seam heat-sealed, mechanical end folds formed, and the packages equally spaced and timed from one another. The conventional end fold sealer employs continuous, low stick sealing belts both for transporting the Packaged articles from the overwrapping machine and for heating and cooling the package to seal the end folds.
A drawback of the continuous sealing belts of the conventional end fold sealer is that the speed of the sealing belt travel must be greater than the overwrapping machine's speed of producing packages in order to take away the packages quickly enough to avoid damage by allowing the packages to accumulate or come in contact with the overhead grippers or pusher plates of the overwrapping machine. The higher speed of the sealing belts facilitates the package take away but requires extending the length of the conventional end fold sealing line with resultant higher costs.
The conventional package end fold sealer utilizes a series of individual heater blocks and long flat cooling plates adjacent the sealing belts to heat, seal and cool the package end folds. Each block must be individually maintained at its proper temperature by thermostatic controllers. Conventionally, 8 to 16 individual electrical heat controllers, along with 16 to 32 heater elements, will be needed. The sealing belts take away the packages from the overwrapper and maintain the end folds of the package adjacent to the package. While the belts transport the package, they first move over the faces of the heating blocks and transfer heat to the packages to form end seals, next the sealing belts move over the cooling plates to cool the formed end seals. At the end of the conventional package end fold sealer the belts release the package and continue the cycle. However, because the same part of the belt is in constant contact with the package end fold througout the sealing process there is a danger that the plastic film will stick to the belt when it releases the package, causing damage to the end fold.
To maintain the effective release of the moving sealing belts it is necessary to frequently coat the belts with a silicone release agent, either by spray atomization or brush. As dust and grime build up on the heater blocks, the heat transfer through the sealing belts is reduced, with resultant defectively sealed packages. Wear on the heater elements, thermostats, and belts results in frequent downtime for replacement.
Although heat transfer may be improved by increasing the pressure of the belts on the package ends, the stiff cardboard tubes on which most paper products are wound causes increased belt wear as the pressure is increased.
Heated air has been used for sealing the length seams of polyethylene packages where only two layers of plastic overlap. Hot air alone, however, cannot properly seal the package end fold, as the plastic shrinks away from the heat resulting in a separation of the top flaps of a mechanical end fold from the lower flaps.
What is needed is a package end fold sealer that can produce properly formed end fold seals at a high rate of speed without the need for heated moving belts and heating blocks which is thus easier to maintain and operate.